Various aqueous fluids are commonly introduced into wellbores in order to perform drilling, completion and workover operations. Such fluids must perform a number of functions, including: (1) providing sufficient hydrostatic pressure to prevent formation fluids from entering the wellbore, (2) cleaning the hole with reasonable pump pressures and annular velocities, (3) preventing excessive fluid [filtrate or whole fluid] losses to the formation, (4) remaining stable at the maximum well temperature, (5) providing maximum protection against formation damage, and (6) having environmentally acceptable properties. Fluids, which meet these requirements typically, are aqueous solutions of one or more soluble salts including potassium chloride, sodium chloride, calcium chloride, sodium bromide, calcium bromide or zinc bromide, having densities up to and beyond 19.2 pounds per gallon.
After aqueous fluids are introduced into a wellbore, the fluids may be exposed to hydrocarbons, particularly those produced from the formation in the pay zone. Contamination of aqueous fluids by such hydrocarbons may lead to the formation of stable water-in-oil emulsions. The emulsions, which often are highly viscous and gel like, may develop emulsion blockages in the producing formation, thus diminishing the capability of the well to produce.
Water-in-oil emulsions can be broken by various physical methods, including heating, centrifugation, electrostatic precipitation and filtration, however none of these physical methods is feasible for use downhole. As a result, chemical additives are needed which effectively prevent or resolve downhole emulsions in aqueous solutions, such as brines, without the need for physical stimulation.